Abstract-This paper describes a novel type of CD-ROM drive which can automatically distinguish between two basic operating modes: continuous playback and continuous access. The drive, based on the adaptive-speed technology, is optimized for a very high data throughput during sustained read-out using a new cubic overspeed profile. In addition, by detecting the state of continuous access and switching the spindle motor into a CAV (constant angular velocity) loop, the drive features very low power consumption. Two dedicated firmware algorithms which can detect one of the two operating modes either at the bit-engine level or at the data-path level are also presented. While implementing the algorithm at the data-path level, the paper will also approach a novel technique for the optimization of the data flow via controlling the speed of the spindle motor. A better buffer management can therefore be achieved. Last but not least, the cubic overspeed profile is shown to be optimal not only for sustained playback but also while the drive is performing either a unique seek action or a short sequence of seeks.
Abstract-As the performance of the CD-ROM drives continues t o increase, special attention should be paid t o any element in the system that disturbs the desired specifications. When very low access times are considered, it will be mandatory t o reach the target track within only one seek action, i.e. without any consequent retry or correction seek. Many CD-ROM drives count the tracks crossed during seeking and, by comparing this count with the pre-calculated seek length, the exact target location can be detected. This paper considers the error that affects the track-counting mechanism due t o the rotating disc spiral. It will be shown that, for a given seek length, the number of crossed tracks differs between outside-and inside-oriented seeks. The involved equations will be derived and an algorithm will be proposed for determining the correct number of tracks t o be crossed during a seek action. The proposed algorithm, which is optimized for microprocessor implementation, relies on two look-up tables and a learning scheme that allows look-ahead seek correction for both spiral rotation and system tolerances.
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